U.S. patent number 6,054,910 [Application Number 09/260,271] was granted by the patent office on 2000-04-25 for dielectric filter having an inner conductor with two open-circuited inner ends.
This patent grant is currently assigned to Murata Manufacturing Co., Ltd.. Invention is credited to Hiromi Ogura, Hitoshi Tada.
United States Patent |
6,054,910 |
Tada , et al. |
April 25, 2000 |
Dielectric filter having an inner conductor with two open-circuited
inner ends
Abstract
A dielectric filter comprising: a dielectric block including a
first elongated sub-block and a second elongated sub-block each
having a corresponding pair of longitudinally opposing end faces,
and an outer surface, said sub-blocks being disposed adjacent one
another; a first longitudinally extending through-hole disposed
between the first pair of longitudinally opposing end faces of said
first sub-block, the first through-hole having two outer ends and
an inner surface; a first inner conductor formed on the inner
surface of said first through-hole, said first inner conductor
having outer ends; an outer conductor formed on the outer surface
of said dielectric block but not electrically coupled to the outer
ends of the first inner conductor such that the outer ends of the
first inner conductor are open-circuited; a first connection
conductor through which a predetermined part of the first inner
conductor between its outer ends is connected to said outer
conductor; a second longitudinally extending through-hole disposed
between the second pair of longitudinally opposing end faces of
said second sub-block, the second through-hole having two outer
ends and an inner surface; a second inner conductor formed on the
inner surface of said second through-hole, said second inner
conductor being electrically connected to said outer conductor at
its outer ends such that they are short-circuited, said inner
conductor having a pair of open-circuited inner ends disposed at a
predetermined location between its two outer ends, wherein said
first and second sub-blocks of said dielectric block are
longitudinally shifted relative to one another.
Inventors: |
Tada; Hitoshi (Ishikawa-ken,
JP), Ogura; Hiromi (Ishikawa-ken, JP) |
Assignee: |
Murata Manufacturing Co., Ltd.
(JP)
|
Family
ID: |
18151691 |
Appl.
No.: |
09/260,271 |
Filed: |
March 2, 1999 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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761984 |
Dec 11, 1996 |
5912603 |
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Foreign Application Priority Data
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Dec 12, 1995 [JP] |
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7-323154 |
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Current U.S.
Class: |
333/206;
333/222 |
Current CPC
Class: |
H01P
1/2056 (20130101) |
Current International
Class: |
H01P
1/20 (20060101); H01P 1/205 (20060101); H01P
001/202 (); H01P 007/04 () |
Field of
Search: |
;333/202,206,222 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0645836 |
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Mar 1995 |
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EP |
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62-38601 |
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Feb 1987 |
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JP |
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64-69102 |
|
Mar 1989 |
|
JP |
|
2241203 |
|
Aug 1990 |
|
JP |
|
451602 |
|
Feb 1992 |
|
JP |
|
4150101 |
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May 1992 |
|
JP |
|
Other References
Patents Abstracts of Japan--E-1257 Sep. 2, 1992, vol. 16/No.
415..
|
Primary Examiner: Pascal; Robert
Assistant Examiner: Summons; Barbara
Attorney, Agent or Firm: Ostrolenk, Faber, Gerb &
Soffen, LLP
Parent Case Text
This is a division of application Ser. No. 08/761,984, filed Dec.
11, 1996, now U.S. Pat. No. 5,912,603.
Claims
What is claimed is:
1. A dielectric filter, comprising:
a dielectric block including a first elongated sub-block and a
second elongated sub-block each having a corresponding pair of
longitudinally opposing end faces, and an outer surface, said
sub-blocks being disposed adjacent one another;
a first longitudinally extending through-hole disposed between the
first pair of longitudinally opposing end faces of said first
sub-block, the first through-hole having two outer ends and an
inner surface;
a first inner conductor formed on the inner surface of said first
through-hole, said first inner conductor having outer ends;
an outer conductor formed on the outer surface of said dielectric
block but not electrically coupled to the outer ends of the first
inner conductor such that the outer ends of the first inner
conductor are open-circuited;
a first connection conductor through which a predetermined part of
the first inner conductor between its outer ends is connected to
said outer conductor;
a second longitudinally extending through-hole disposed between the
second pair of longitudinally opposing end faces of said second
sub-block, the second through-hole having two outer ends and an
inner surface;
a second inner conductor formed on the inner surface of said second
through-hole, said second inner conductor being electrically
connected to said outer conductor at its outer ends such that they
are short-circuited, said second inner conductor having a pair of
open-circuited inner ends disposed at a predetermined location
between its two outer ends,
wherein said first and second sub-blocks of said dielectric block
are longitudinally shifted relative to one another.
2. The dielectric filter of claim 1, wherein the second inner
conductor further comprises a gap defining the pair of
open-circuited inner ends disposed at the predetermined location
between its two outer ends.
3. The dielectric filter of claim 2, wherein the gap separates
respective first and second portions of the second inner
conductor.
4. The dielectric filter of claim 2, wherein the gap defines a
capacitor coupled between first and second portions of the second
inner conductor.
5. The dielectric filter of claim 2, wherein the gap is defined by
an absence of conductive material in the second inner
conductor.
6. The dielectric filter of claim 2, wherein the gap is defined by
an isolation wall formed from the dielectric material of the second
sub-block and an absence of conductive material in the second inner
conductor.
7. The dielectric filter of claim 6, wherein the isolation wall
interrupts the second longitudinally extending through hole and
defines respective closed ends of the first and second portions of
the second inner conductor.
8. The dielectric filter of claim 1, wherein said dielectric block
further includes a laterally extending through-hole extending from
said predetermined part of said first inner conductor to the outer
surface of said dielectric block, and said first connection
conductor is disposed in said laterally extending through-hole.
9. The dielectric filter of claim 1, wherein respective distances
between corresponding pairs of opposing end faces define respective
lengths of the sub-blocks, the lengths of the sub-blocks being
substantially equal.
10. The dielectric filter of claim 9, wherein the adjacent
sub-blocks are longitudinally shifted from one another by an amount
about equal to one half the lengths of the sub-blocks.
11. The dielectric filter of claim 1, wherein at least one
sub-block further comprises a laterally disposed hole extending
from a central part of its longitudinally extending through-hole to
its outer surface, the laterally disposed hole including the first
connection conductor which electrically communicates with the first
inner conductor of the first longitudinally extending through-hole
and the outer conductor of the dielectric block.
12. The dielectric filter of claim 11, wherein:
a first part of the first sub-block extending from one end face to
about the laterally disposed hole defines a first resonator;
a second part of the first sub-block extending from the other end
face to about the laterally disposed hole defines a second
resonator, the first and second resonators being in series and
joined at a common node; and
the laterally disposed hole and connection conductor define a shunt
inductor coupled from the common node to the outer conductor.
13. The dielectric filter of claim 1, wherein the outer conductor
covers substantially the entire outer surface of the dielectric
block except for the end faces of the first sub-block.
14. The dielectric filter of claim 13, further comprising an
electrically conductive electrode disposed on and covering a
portion of one of the end faces of the first sub-block, the
electrode being proximate to the first through-hole at the end face
and being electrically connected to the first inner conductor but
electrically insulated from the outer conductor.
15. The dielectric filter of claim 14, wherein the electrically
conductive electrode is an input electrode.
16. The dielectric filter of claim 1, wherein the outer conductor
covers substantially the entire outer surface of the dielectric
block except respective portions of at least one end face of at
least one sub-block.
17. The dielectric filter of claim 16, further comprising a
plurality of electrically conductive electrodes, each electrode
being: (i) disposed on and covering only part of the respective
portion of a respective end face, (ii) proximate to the respective
through-hole at the respective end face, and (iii) electrically
connected to the respective inner conductor of the respective
through-hole but electrically insulated from the outer
conductor.
18. The dielectric filter of claim 17, wherein at least one of the
electrically conductive electrodes is an input electrode.
19. The dielectric filter of claim 18, wherein at least one of the
electrically conductive electrodes is an output electrode.
20. The dielectric filter of claim 1, wherein the dielectric block
is formed of a ceramic material.
21. The dielectric filter of claim 1, wherein the inner conductors
and outer conductor are formed of an electrically conductive
material.
22. The dielectric filter of claim 21, wherein the inner conductors
and outer conductor are formed of copper.
23. The dielectric filter of claim 1, wherein the sub-blocks are
integrally formed.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dielectric filter, and more
particularly, to a dielectric filter suitable for use as a
band-elimination filter in a mobile communication device or the
like.
2. Description of the Related Art
FIG. 36 illustrates a conventional band-elimination filter
including a dielectric resonator 121, a coupling capacitor 122, and
a lead terminal 123 connecting the coupling capacitor 122 to the
dielectric resonator 121.
The dielectric resonator 121 is composed of a rectangular
dielectric block 124 having a through-hole 125. The inner wall of
the through-hole 125 is covered with an inner conductor 126. The
outer surface of the dielectric block 124 is covered with an outer
conductor 127. One end of the inner conductor 126 is connected to
the outer conductor 127. The coupling capacitor 122 is composed of
a dielectric substrate 128 having capacitor electrodes 129 and 130
formed on either side of the dielectric substrate 128.
The inner conductor of the dielectric resonator 121 is connected to
one capacitor electrode 129 of the coupling capacitor 122 via the
lead terminal 123. The other capacitor electrode 130 of the
coupling capacitor 122 is connected to a signal line disposed on a
circuit board. The outer conductor 127 is connected to a ground
line disposed on the circuit board. The dielectric filter having
the above structure acts as a band-elimination filter with an
equivalent circuit shown in FIG. 37.
As described above, the conventional dielectric filter includes not
only the dielectric resonator 121 but also the coupling capacitor
122 and the lead terminal 123. As a result, troublesome
manipulation is required to mount a dielectric filter of this type
on a circuit board.
FIG. 38 illustrates a typical frequency characteristic obtained in
a conventional dielectric filter of the type described above. As
can be seen from FIG. 38, the dielectric filter has a simple trap
frequency ft with no attenuation in frequency bands around the trap
frequency ft. Therefore, when it is desirable that the filter have
attenuation property in a frequency band either higher or lower
than the trap frequency, it is required to couple the filter with
another dielectric filter acting as a band-pass filter. This makes
it more difficult to mount the filters.
SUMMARY OF THE INVENTION
Thus, it is an object of the present invention to provide a
dielectric filter which acts not only as a band-elimination filter
but also as a band-pass filter exhibiting attenuation at the edges
of the pass-bands at higher and lower frequencies than the trap
frequency and which can be easily mounted on a circuit board.
To achieve the above object, the present invention provides a
dielectric filter with various features and aspects as described
below. According to a first aspect of the present invention, there
is provided a dielectric filter including: a dielectric block
having a pair of opposing end faces; a through-hole formed between
the pair of opposing end faces of the dielectric block; an inner
conductor formed on the inner surface of the through-hole, the
inner conductor being open-circuited at both its ends; an outer
conductor formed on the outer surface of the dielectric block; and
a connection conductor by which a central part of the inner
conductor between its two opposing ends is connected to the outer
conductor.
In this dielectric filter, an inductor is formed by the connection
conductor by which the central part of the inner conductor between
its two opposing ends is connected to the outer conductor. This
allows the dielectric filter to behave as a band-elimination filter
having band-pass characteristics at frequencies higher and lower
than a trap frequency wherein elimination occurs at both band edges
of the pass-bands.
According to a second aspect of the present invention based on the
above first aspect, there is provided a dielectric filter in which
the dielectric block further includes a side-wall through-hole
extending from the central part of the inner surface between the
two opposing ends of the through-hole to the outer surface of the
dielectric block, and the above-described connection conductor is
disposed in this side-wall through-hole.
In this dielectric filter, since the connection conductor is
disposed in the side-wall through-hole, it is possible for the
inductor to have a stable inductance.
According to a third aspect of the present invention, there is
provided a dielectric filter including: a dielectric block
including a plurality of sub-blocks each having a pair of opposing
end faces; a plurality of through-holes formed between the pairs of
opposing end faces of the respective sub-blocks of the dielectric
block; a plurality of inner conductors formed on the inner surfaces
of the plurality of through-holes, the plurality of inner
conductors being open-circuited at their both ends; an outer
conductor formed on the outer surface of the dielectric block; and
a plurality of connection conductors by which the central parts of
the respective inner conductors between their two opposing ends are
connected to the outer conductor, wherein the plurality of
sub-blocks of the dielectric block are shifted in position relative
to one another toward either of the pair of opposing ends.
In this arrangement, the dielectric filter is composed of a
plurality of filter stages in which the respective sub-blocks of
the dielectric block are shifted in position relative to one
another toward either of the pair of the opposing ends thereby
avoiding undesirable coupling among the filter stages. This
structure allows the trap band to have greater attenuation and also
allows the frequency bandwidth of the trap band to be adjusted to a
desired value. Thus, it is possible to realize a high-performance
band-elimination filter having band-pass regions at frequencies
higher and lower than a trap frequency wherein elimination occurs
at both band edges of the pass-bands.
According to a fourth aspect of the present invention, there is
provided a dielectric filter including: a dielectric block
including a plurality of sub-blocks each having a pair of opposing
end faces; a plurality of through-holes formed between the pairs of
opposing end faces of the respective sub-blocks of the dielectric
block; a plurality of inner conductors formed on the inner surfaces
of the plurality of through-holes, the plurality of inner
conductors being open-circuited at both their ends; an outer
conductor formed on the outer surface of the dielectric block; and
a plurality of connection conductors by which the central parts of
the respective inner conductors between their two opposing ends are
connected to the outer conductor, wherein the dielectric block is
formed in a rectangular shape, and a coupling-preventing structure
is formed between adjacent sub-blocks in such a manner that the
coupling-preventing structure extends from one end face toward a
central part between the two opposing end faces.
In this arrangement, the dielectric filter is composed of a
plurality of filter stages in which the coupling preventing
structure is provided between adjacent sub-blocks of the dielectric
block thereby preventing undesirable coupling among the filter
stages. This structure allows the trap band to have greater
attenuation and also allows the frequency bandwidth of the trap
band to be adjusted to a desired value. Thus, it is possible to
realize a high-performance band-elimination filter having band-pass
regions at frequencies higher and lower than a trap frequency
wherein elimination occurs at both band edges of the
pass-bands.
According to a fifth aspect of the present invention based on the
above third or fourth aspect, there is provided a dielectric filter
in which the dielectric block further includes a side-wall
through-hole extending from the central part of the through-hole
between its two opposing ends to the outer surface of the
dielectric block, and the connection conductor is disposed in this
side-wall through-hole.
In this dielectric filter, since the connection conductor is
disposed in the side-wall through-hole, it is possible for the
inductor to have a stable inductance.
According to a sixth aspect of the present invention, there is
provided a dielectric filter including: a dielectric block
including a first sub-block and a second sub-block each having its
own pair of opposing end faces; a through-hole formed between the
pair of opposing end faces of the first sub-block of the dielectric
block; an inner conductor formed on the inner surface of the
through-hole, the inner conductor being open-circuited at both its
ends; an outer conductor formed on the outer surface of the
dielectric block; a connection conductor by which a central part of
the inner conductor between its two opposing ends is connected to
the outer conductor; a through-hole formed between the pair of
opposing end faces of the second sub-block of the dielectric block;
and an inner conductor formed on the inner surface of the
through-hole of the second sub-block, the inner conductor being
short-circuited at both its outer ends, the inner conductor having
open-circuited inner ends located at a center between its two outer
ends; wherein the dielectric block is formed in a rectangular
shape, and an electromagnetic coupling preventing structure is
formed between adjacent sub-blocks in such a manner that the
electromagnetic coupling preventing structure extends from one end
face toward a central part between the two opposing end faces.
In this arrangement, the dielectric filter is composed of a
plurality of filter stages in which an electromagnetic
coupling-preventing structure is provided between adjacent
sub-blocks of the dielectric block thereby preventing undesirable
coupling among the filter stages. This structure allows the trap
band to have greater attenuation and also allows the frequency
bandwidth of the trap band to be adjusted to a desired value. Thus,
it is possible to realize a high-performance band-elimination
filter having band-pass regions at frequencies higher and lower
than a trap frequency wherein elimination occurs at both band edges
of the pass-bands.
According to a seventh aspect of the present invention, there is
provided a dielectric filter including: a dielectric block
including a first sub-block and a second sub-block each having its
own pair of opposing end faces; a through-hole formed between the
pair of opposing end faces of the first sub-block of the dielectric
block; an inner conductor formed on the inner surface of the
through-hole, the inner conductor being open-circuited at both its
ends; an outer conductor formed on the outer surface of the
dielectric block; a connection conductor by which a central part of
the inner conductor between its two opposing ends is connected to
the outer conductor; a through-hole formed between the pair of
opposing end faces of the second sub-block of the dielectric block;
and an inner conductor formed on the inner surface of the
through-hole of the second sub-block, the inner conductor being
short-circuited at both its outer ends, the inner conductor having
open-circuited inner ends located at a center between its two outer
ends; wherein the plurality of sub-blocks of the dielectric block
are shifted in position relative to one another toward either of
the pair of opposing ends.
In this arrangement, the dielectric filter is composed of a
plurality of filter stages in which the respective sub-blocks of
the dielectric block are shifted in position relative to one
another toward either of the pair of the opposing ends thereby
preventing undesirable coupling among the filter stages. This
structure allows the trap band to have greater attenuation and also
allows the frequency bandwidth of the trap band to be adjusted to a
desired value. Thus, it is possible to realize a high-performance
band-elimination filter having band-pass regions at frequencies
higher and lower than a trap frequency wherein elimination occurs
at both band edges of the pass-bands.
According to an eighth aspect of the present invention, based on
the above sixth or seventh aspect, the dielectric block further
includes a side-wall through-hole extending from the central part
of the through-hole between its two opposing ends to the outer
surface of the dielectric block, and the connection conductor is
disposed in this side-wall through-hole.
In this dielectric filter, since the connection conductor is
disposed in the side-wall through-hole, it is possible for the
inductor to have a stable inductance.
Other features and advantages of the present invention will become
apparent from the following description of the invention which
refers to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a first embodiment of a dielectric
filter according to the present invention;
FIG. 2 is a cross-sectional view of the dielectric filter of FIG. 1
taken along line 2--2;
FIG. 3 is a circuit diagram of an equivalent circuit of the
dielectric filter shown in FIG. 1;
FIG. 4 is a graph illustrating the frequency characteristic of the
dielectric filter shown in FIG. 1;
FIG. 5 is a schematic diagram illustrating a modification of the
dielectric filter of FIG. 1;
FIG. 6 is a schematic diagram illustrating another modification of
the dielectric filter of FIG. 1;
FIG. 7 is a schematic diagram illustrating still another
modification of the dielectric filter of FIG. 1;
FIG. 8 is a perspective view of a second embodiment of a dielectric
filter according to the present invention;
FIG. 9 is a plan view of the dielectric filter shown in FIG. 8;
FIG. 10 is a circuit diagram of an equivalent circuit of the
dielectric filter shown in FIG. 8;
FIG. 11 is a graph illustrating the frequency characteristic of the
dielectric filter shown in FIG. 8;
FIG. 11a-11c are views showing a sub-block of FIG. 8 having a
modified end face;
FIG. 11d is a plan view of an alternative embodiment of FIG. 8;
FIG. 12 is a perspective view of a third embodiment of a dielectric
filter according to the present invention;
FIG. 13 is a plan view of the dielectric filter shown in FIG.
12;
FIG. 14 is a circuit diagram of an equivalent circuit of the
dielectric filter shown in FIG. 12;
FIG. 15 is a graph illustrating the frequency characteristic of the
dielectric filter shown in FIG. 12;
FIG. 16 is a perspective view of a fourth embodiment of a
dielectric filter according to the present invention;
FIG. 17 is a plan view of the dielectric filter shown in FIG.
16;
FIG. 18 is a circuit diagram of an equivalent circuit of the
dielectric filter shown in FIG. 16;
FIG. 19 is a graph illustrating the frequency characteristic of the
dielectric filter shown in FIG. 16;
FIG. 20 is a perspective view of a fifth embodiment of a dielectric
filter according to the present invention;
FIG. 21 is a plan view of the dielectric filter shown in FIG.
20;
FIG. 22 is a cross-sectional view of the dielectric filter of FIG.
20 taken along line 22--22;
FIG. 23 is a circuit diagram of an equivalent circuit of the
dielectric filter shown in FIG. 20;
FIG. 24 is a graph illustrating the frequency characteristic of the
dielectric filter shown in FIG. 20;
FIG. 25 is a fragmentary plan view illustrating a modification of
the dielectric filter shown in FIG. 20;
FIG. 26 is a cross-sectional view of the dielectric filter of FIG.
25 taken along line 26--26;
FIG. 27 is a perspective view of a sixth embodiment of a dielectric
filter according to the present invention;
FIG. 28 is a plan view of the dielectric filter shown in FIG.
27;
FIG. 29 is a cross-sectional view of the dielectric filter of FIG.
28 taken along line 29--29;
FIG. 30 is a circuit diagram of an equivalent circuit of the
dielectric filter shown in FIG. 27;
FIG. 31 is a graph illustrating the frequency characteristic of the
dielectric filter shown in FIG. 27;
FIG. 32 is a fragmentary plan view illustrating a modification of
the dielectric filter shown in FIG. 27;
FIG. 33 is a cross-sectional view of the dielectric filter of FIG.
32 taken along line 33--33;
FIG. 34 is a perspective view of a dielectric filter having a
similar equivalent circuit and similar characteristics to those of
the dielectric filter according to the third embodiment shown in
FIGS. 12 and 13;
FIG. 35 is a perspective view of a dielectric filter having a
similar equivalent circuit and similar characteristics to those of
the dielectric filter according to the sixth embodiment shown in
FIGS. 27 and 28;
FIG. 36 is an exploded perspective view of a conventional
dielectric filter;
FIG. 37 is a circuit diagram of an equivalent circuit of the
dielectric filter shown in FIG. 36; and
FIG. 38 is a graph illustrating the frequency characteristic of the
dielectric filter shown in FIG. 36.
DESCRIPTION OF EMBODIMENTS OF THE INVENTION
With reference to specific embodiments of dielectric filters, the
present invention will be described in further detail below in
conjunction with the accompanying drawings.
FIG. 1 is a perspective view of a first embodiment of a dielectric
filter 100 according to the present invention. FIG. 2 is a
cross-sectional view taken along line 2--2 of FIG. 1. As shown in
these figures, the dielectric filter includes a rectangular
dielectric block 1 made up of a ceramic material. The dielectric
block 1 has two opposing end faces 1a and 1b. A through-hole 2 is
formed between these end faces 1a and 1b. An inner conductor 3 is
formed on the inner wall of the through-hole 2. An outer conductor
4 is formed over the whole outer surface of the dielectric block 1
except its end faces 1a and 1b. In this structure, the inner
conductor 3 is not connected, at either end, to the outer conductor
4 and thus the inner conductor 3 is electrically open-circuited at
both its ends. The inner conductor 3 and the outer conductor 4 may
be formed, for example, by disposing an electrode material such as
Cu over the whole surface of the dielectric block 1 including the
inner wall of the through-hole 2 by means of electroless plating or
the like, and then removing the electrode material from the end
faces 1a and 1b.
The dielectric block 1 also has a side-wall through-hole 5
extending from a central part of the inner wall of the through-hole
2 between its two opposing ends to the outer surface of the
dielectric block 1. A connection conductor 6 is formed on the inner
wall of the side-wall through-hole 5 so that the central part of
the inner conductor 3 between the two opposing ends is connected to
the outer conductor 4 via the connection conductor 6. This
connection conductor 6 may be formed at the same time as the inner
conductor 3 and the outer conductor 4 by subjecting the side-wall
through-hole 5 to the plating process for forming the inner
conductor 3 and the outer conductor 4.
In the dielectric filter having the structure described above, one
end of the inner conductor 3 is connected to a signal line while
the other end is electrically open-circuited. The outer conductor 4
is connected to a ground line. Thus, the dielectric filter of the
present embodiment can be represented by an equivalent circuit
shown in FIG. 3. In this equivalent circuit, R1 and R2 are two
resonators formed with the inner conductor 3 divided into two
sections at the center between the two opposing ends, and L1 is an
inductor associated with the connection conductor 6, which is
grounded. The dielectric filter represented by the above equivalent
circuit has two band-pass regions separated by a trap frequency ft,
as shown in FIG. 4, wherein attenuation occurs at both band edges
of the pass-bands. The trap frequency ft and the
frequency-attenuation characteristics of the two band-pass regions
located at either side of the trap frequency ft are determined by
properly selecting the relative dielectric constant of the
dielectric block 1, the length of the inner conductor 3, and the
inductance associated with the connection conductor 6. As described
above, the dielectric filter with the above structure behaves both
as a band-pass filter and a band-elimination filter with two
band-pass regions separated by the trap frequency ft.
In an alternative mode, as shown in FIG. 5, one end of the inner
conductor 3 may be connected to an end face electrode 8 formed on
the end face 1a in an area surrounding the through-hole 2, and the
other end of the inner conductor 3 may be connected to an end face
electrode 9 formed on the end face 1b in an area surrounding the
through-hole 2. In this case, the outer conductor 4 has additional
portions extending onto the end faces 1a and 1b wherein gaps 10 and
11 are formed around the respective end face electrodes 8 and 9 so
that the end face electrodes 8 and 9 are electrically isolated from
the portions of the outer conductor 4 on the end faces 1a and 1b.
This structure, in which the inner conductor 3 is connected to the
end face electrodes 8 and 9, readily permits a signal line to be
connected to the inner conductor 3. That is, the connection can be
accomplished simply by connecting the signal line to the end face
electrode 8 or the end face electrode 9. Furthermore, in the case
where the outer conductor 4 is formed by means of plating, the
above structure allows the conductors to be more easily formed,
because this structure leads to a reduction in the area of the
electrode material which must be removed after the plating
process.
Alternatively, as shown in FIG. 6, the inner conductor 3 may be
connected to end face electrodes 12 and 13 wherein the end face
electrode 12 has a portion extending across the end face 1a
surrounding the through-hole 2 and further extending onto the lower
side of the dielectric block 1, while the end face electrode 13 has
a portion extending across the end face 1b surrounding the
through-hole 2 and further extending onto the lower side of the
dielectric block 1. Also in this case, the outer conductor 4 has
additional portions extending onto the end faces 1a and 1b wherein
gaps 14 and 15 are formed around the respective end face electrodes
12 and 13 so that the end face electrodes 12 and 13 are
electrically isolated from the portions of the outer conductor 4 on
the end faces 1a and 1b. This structure, in which the inner
conductor 3 is connected to the end face electrodes 12 and 13 in
the above-described manner, even more readily permits a signal line
to be connected the inner conductor 3 than in the structure shown
in FIG. 5, because the connection can be accomplished simply by
connecting the signal line to the lower-side portion of the end
face electrode 12 or the lower-side portion of the end face
electrode 13. Furthermore, in the case where the outer conductor 4
is formed by means of plating, the above structure allows the
conductors to be easily formed as in the case of the structure
shown in FIG. 5, because this structure also leads to a reduction
in the area of the electrode material which should be removed after
the plating process.
In still another alternative mode, shown in FIG. 7, the inner
conductor 3 may also be formed in such a manner as to have a length
which does not reach either the end face 1a or the end face 1b. In
this case, the outer conductor 4 is formed in such a manner as to
extend over the whole area of the end face 1a and 1b, respectively,
and further to extend into the through-hole 2. The portions of the
outer conductor 4 located on the inner wall of the through-hole 2
are electrically isolated from the inner conductor 3 by gaps 16 and
17. This structure in which the outer conductor 4 is formed in the
above-described manner leads to an improvement in the shielding
performance of the dielectric filter.
In the above structures, the side-wall through-hole 5 is formed, as
described above, in such a manner as to extend from a central part
of the inner wall of the through-hole 2 between its two opposing
ends to the outer surface of the dielectric block 1, and the
connection conductor 6 is formed on the inner wall of the side-wall
through-hole S in such a manner that the central part of the inner
conductor 3 between the two opposing ends is connected to the outer
conductor 4 via the connection conductor 6.
As referred to herein, the "central part" between the two ends is
not required to be located at the exact geometric center but may be
located within a range around the exact geometric center as long as
the filter has a good frequency characteristic which obtains the
objects of the invention.
FIG. 8 is a perspective view of a second embodiment of a dielectric
filter 200 according to the present invention, while a plan view
thereof is shown in FIG. 9. As shown in these figures, the
dielectric filter is composed of a dielectric block 21 made up of a
ceramic material including two sub-blocks LW1 and LW2 formed in an
integral fashion. Sub-blocks LW1 and LW2 have equal lengths LE1 and
LE2 and equal widths W1 and W2 wherein sub-blocks LW1 and LW2 are
shifted in position along their longitudinal directions relative to
each other by half the length LE1 or LE2.
The sub-block LW1 has two opposing end faces, namely a first end
face 21a and a second end face 21b, located at either end of the
length LE1, and also has two opposing sides, namely an upper face
21c and a lower face 21d, which are perpendicular to the end faces
21a and 21b. Similarly, the sub-block LW2 has two opposing end
faces, namely a first end face 21e and a second end face 21f,
located at either end of the length LE2, and also has two opposing
sides, namely an upper face 21g and a lower face 21h, which are
perpendicular to the end faces 21e and 21f. The first end faces 21a
and 21e of the respective sub-blocks LW1 and LW2 are both located
on one side of the dielectric filter 200, while the second end
faces 21b and 21f are both located on the other side. The upper
faces 21c and 21g of the respective sub-blocks LW1 and LW2 lie in
one plane, and the lower faces 21d and 21h lie in another
plane.
The dielectric block 21 has a through-hole 22 formed between the
first and second end faces 21a and 21b of the sub-block LW1 and
also has a through-hole 23 formed between the first and second end
faces 21e and 21f of the sub-block LW2. Inner conductors 24 and 25
are formed on the inner walls of the respective through-holes 22
and 23. An outer conductor 26 is formed over the whole outer
surface of the dielectric block 21 except the end faces 21a, 21b,
21e, and 21f. In this structure, the inner conductors 24 and 25 are
not connected, at either end, to the outer conductor 26, and thus
each of inner conductors 24 and 25 are electrically open-circuited
at their ends. The inner conductors 24, 25 and the outer conductor
26 may be formed, for example, by disposing an electrode material
such as Cu over the whole surface of the dielectric block 21
including the inner walls of the through-holes 22, 23 using
electroless plating or the like, and then removing the electrode
material from the end faces 21a, 21b, 21e, and 21f.
The dielectric block 21 has a side-wall through-hole 27 extending
from a central part of the inner wall of the through-hole 22
between its two opposing ends to the upper surface 21c (where upper
surface 21c is a part of the outer surface of the dielectric block
21). Dielectric block 21 also has a side-wall through-hole 28
extending from a central part of the inner wall of the through-hole
23 between its two opposing ends to the upper surface 21g (where
upper surface 21g is also a part of the outer surface of the
dielectric block 21). Connection conductors 29 and 30 are formed on
the inner walls of the respective side-wall through-holes 27 and 28
so that the central parts of the respective inner conductors 24 and
25 between the two opposing ends are connected to the outer
conductor 26 via the connection conductors 29 and 30. These
connection conductors 29 and 30 may be formed at the same time as
the inner conductors 24 and 25 and the outer conductor 26 by
subjecting the side-wall through-holes 27 and 28 to the plating
process for forming the inner conductors 24 and 25 and the outer
conductor 26.
In the dielectric filter having the structure described above, the
end of the inner conductor 24 on the side of the first end face 21a
of the sub-block LW1 is used as an input terminal IN, while the end
of the inner conductor 25 on the side of the second end face 21f of
the sub-block LW2 is used as an output terminal OUT, as shown in
FIG. 9. The outer conductor 26 is connected to a ground line. Thus,
the dielectric filter of the present embodiment can be represented
by an equivalent circuit shown in FIG. 10.
In this equivalent circuit, R3 and R4 are two resonators formed
with the inner conductor 24 of the sub-block LW1 divided into two
sections at the center between its two opposing ends, and R5 and R6
are two resonators formed with the inner conductor 25 of the
sub-block LW2 divided into two sections at the center between its
two opposing ends. L2 is an inductor associated with the connection
conductor 29 of the sub-block LW1, and L3 is an inductor associated
with the connection conductor 30 of the sub-block LW2. K35 is a
phase shifter formed between a part of the sub-block LW1 in the
region extending from the first end face 21a to the connection
conductor 29 and a part of the sub-block LW2 in the region
extending from the second end face 21f to the connection conductor
30.
As described above, the dielectric filter includes: the dielectric
block 21 composed of the sub-block LW1 with two opposing end faces
namely the first end face 21a and the second end face 21b, and the
sub-block LW2 with two opposing end faces namely the first end face
21e and the second end face 21f; the two through-holes 22 and 23,
one of which is formed between the first end face 21a and the
second end face 21b of the sub-block LW1 of the dielectric block
21, while the other one is formed between the first end face 21e
and the second end face 21f of the sub-block LW2; the two inner
conductors 24 and 25 formed on the inner walls of the respective
through-holes 22 and 23 wherein both ends of each inner conductor
24, 25 are electrically open-circuited; the outer conductor 26
formed on the outer surface of the dielectric block 21; and the two
connection conductors 29 and 30 by which the central parts of the
respective inner conductors 24 and 25 are connected to the output
conductor 26. As shown in FIG. 10, two filter stages are formed in
the dielectric filter having the above structure (a first filter
stage is composed of the resonators R3 and R4 and the inductor L2
while a second filter stage is composed of the resonators R5 and R6
and the inductor L3). One filter stage is connected to the input
terminal IN and the other filter stage is connected to the output
terminal OUT. Furthermore, these two filter stages are connected to
each other via the phase shifter K35. Therefore, in this dielectric
filter having the above structure, the signal input at the input
terminal IN is changed in phase by about 90.degree. via the phase
shifter K35, and thus the phase-shifted signal appears at the
output terminal OUT.
The dielectric filter with the above structure has two pass-bands
separated by a trap frequency ft, as shown in FIG. 11, wherein
attenuation occurs at the upper and lower edges of both of the
pass-bands. The trap frequency ft and the frequency-attenuation
characteristics of the two band-pass regions located at either side
of the trap frequency ft are determined by properly selecting the
relative dielectric constant of the dielectric block 21, the
lengths of the inner conductors 24 and 25, and the inductances
associated with the connection conductors 29 and 30. Since the
dielectric filter of the present embodiment has two filter stages,
it is possible to adjust the frequency bandwidth of the trap band,
and a greater attenuation can be achieved within the trap band.
Thus, this dielectric filter acts as a high-performance
band-elimination filter having two pass-bands at either side of the
trap frequency ft. In other words, the dielectric filter behaves
both as a band-pass filter and a band-elimination filter.
As shown in FIGS. 11a and 11b, end face electrodes similar to those
shown in FIG. 5 or 6 may be formed on the end face 21a of the
sub-block LW1 such that the end face electrode on the end face 21a
is connected to the inner conductor 24 to serve as an input
terminal IN. End face 21f of sub-block LW2 may be modified in the
same way such that the end face electrode on the end face 21f is
connected to the inner conductor 25 to serve as an output terminal
OUT. In this case, as in the example shown in FIG. 5 or 6, the
outer conductor 26 may have additional portions which extend onto
the end faces 21a and 21f and which are electrically isolated from
the end face electrodes. The other end faces may be covered with
portions extending from the outer conductor 26 as shown in FIG. 7
see, for example, FIG. 11c. The addition of these end face
electrodes readily permits a signal line to be connected to the
inner conductors. That is, the connection can be accomplished
simply by connecting the signal line to the respective end face
electrodes serving as the input terminal IN and the output terminal
OUT. Furthermore, in the case where the outer conductor 26 is
formed by means of plating, the above structures having the end
face electrodes allow the conductors to be more easily formed,
because these structures lead to a reduction in the area of the
electrode material which should be removed after the plating
process.
In another alternative mode, as in the example shown in FIG. 7, the
inner conductors 24 and 25 may also be formed in such a manner as
to have a length which does not reach either the first end faces
21a, 21e or the second end faces 21b, 21f. In this case, the outer
conductor 26 may be formed in such a manner as to have additional
portions which extend over the whole area of the first end faces
21a, 21e and the second end faces 21b, 21f and which further extend
into the through-holes 22 and 23. This structure leads to an
improvement in the shielding performance of the dielectric
filter.
In the above structures, the side-wall through-holes 27 and 28 are
formed, as described above, in such a manner as to extend from the
corresponding central parts of the inner walls of the through-holes
22 and 23 between their two opposing ends to the outer surface of
the dielectric block 21, and the connection conductors 29 and 30
are formed on the inner walls of the respective side-wall
through-holes 27 and 28 in such a manner that the central parts of
the inner conductors 24 and 25 between the two opposing ends are
connected to the outer conductor 26 via the connection conductors
29 and 30.
As referred to herein, the "central parts" between the two ends are
not required to be located at the exact geometric centers but are
allowed to be located within ranges around the exact geometric
centers as long as the filter has a good frequency characteristic
which obtains the objects of the invention.
As described above, the dielectric block 21 is composed of two
sub-blocks LW1 and LW2 wherein the length LE1 between the first end
face 21a and the second end face 21b of the sub-block LW1 is equal
to the length LE2 between the first end face 21e and the second end
face 21f of the sub-block LW2, and these two sub-blocks LW1 and LW2
are shifted in position in longitudinal directions by half the
length LE1 or LE2 relative to each other. However, these conditions
are not restrictive, and deviations may be made to obtain a
frequency characteristic similar to that shown in FIG. 11. That is,
in the dielectric block 21 of the present embodiment, a certain
tolerance is allowed in the degree to which the length LE1 from the
first end face 21a to the second end face 21b of the sub-block LW1
matches the length LE2 from the first end face 21e to the second
end face 21f of the sub-block LW2. Further, the two sub-blocks LW1
and LW2 may be shifted by half the length LE1 or LE2 relative to
each other in longitudinal directions (toward the opposite end
faces) within a certain tolerance. Similarly, a certain tolerance
is allowed in the degree to which the widths W1 and W2 of the
sub-blocks LW1 and LW2 match.
Reference is now made to FIG. 11d which shows a plan view of an
alternative embodiment of FIG. 8. In this embodiment, sub-block LW1
includes an inner conductor 24 which is not electrically coupled to
the outer conductor 26. Sub-block LW2 includes an inner conductor
25 which is electrically coupled to the outer conductor 26 such
that the inner conductor 25 is short-circuited at both of its ends
to the outer conductor 26. The inner conductor 25 of the second
sub-block LW2 includes a gap 88 at a central part between the two
outer opposing ends 21e, 21f, wherein open circuited inner ends
thereof are formed at the gap 88. A capacitor is formed by the two
facing inner ends across the gap 88.
The gap 88 at the open circuited inner ends of the inner conductor
25 is preferably formed by introducing a protection material before
a plating process so that no electrode material is deposited at the
gap 88. Alternatively, the gap 88 may be formed by partially
removing the electrode material after depositing the material over
the inner wall of the through-hole 23.
It is noted that the gap 88 may be formed by dividing the
through-hole 23 of the second sub-block LW2 into two closed end
holes separated by an isolation wall (see, for example isolation
wall 97 of FIG. 26), wherein the inner surfaces of both portions of
the through-hole 23 are covered with inner conductors.
FIG. 12 is a perspective view of a third embodiment of a dielectric
filter 300 according to the present invention, while a plan view
thereof is shown in FIG. 13. As shown in these figures, the
dielectric filter is composed of a dielectric block 41 made up of a
ceramic material including three sub-blocks LW3, LW4, and LW5 which
are formed in an integral fashion. Sub-blocks LW3, LW4, and LW5
have equal lengths LE3, LE4, and LE5, respectively, and equal
widths W3, W4, and W5, respectively. Sub-blocks LW3, LW4, and LW5
are shifted in longitudinal directions by half the length LE3, LE4,
or LE5 relative to each other.
The sub-block LW3 has two opposing end faces, namely a first end
face 41a and a second end face 41b, located at either end of the
length LE3, and also has two opposing sides, namely an upper face
41c and a lower face 41d, which are perpendicular to the end faces
41a and 41b. Similarly, the sub-block LW4 has two opposing end
faces, namely a first end face 41e and a second end face 41f,
located at either end of the length LE4, and also has two opposing
sides, namely an upper face 41g and a lower face 41h, which are
perpendicular to the end faces 41e and 41f. The sub-block LW5 has
two opposing end faces, namely a first end face 41i and a second
end face 41j, located at either end of the length LE5, and also has
two opposing sides, namely an upper face 41k and a lower face 41l,
which are perpendicular to the end faces 41i and 41j. The first end
faces 41a, 41e, and 41i of the respective sub-blocks LW3, LW4, and
LW5 are located on a same side, while the second end faces 41b,
41f, and 41j are located on another same side. The sub-block LW4
located between the other two sub-blocks is shifted in the
longitudinal direction by half the length LE4 relative to the
sub-blocks LW3 and LW5 toward the end faces 41a and 41i. The upper
faces 41c, 41g, and 41k of the respective sub-blocks LW3, LW4, and
LW5 lie in one plane, and the lower faces 41d, 41h, and 41l lie in
another plane.
The dielectric block 41 has through-holes 42, 43, and 44 wherein
the through-hole 42 is formed between the first and second end
faces 41a and 41b of the sub-block LW3, the through-hole 43 is
formed between the first and second end faces 41e and 41f of the
sub-block LW4, and the through-hole 44 is formed between the first
and second end faces 41i and 41j of the sub-block LW5. Inner
conductors 45, 46, 47 are formed on the inner walls of the
respective through-holes 42, 43, and 44. An outer conductor 48 is
formed over the whole outer surface of the dielectric block 41
except the end faces 41a, 41b, 41e, 41f, 41i, and 41j. In this
structure, the respective inner conductors 45, 46, and 47 are not
connected, at either end, to the outer conductor 48, and thus each
of inner conductors 45, 46, and 47 are electrically open-circuited
at their ends. The inner conductors 45, 46, and 47 and the outer
conductor 48 may be formed, for example, by disposing an electrode
material such as Cu over the whole surface of the dielectric block
41 including the inner walls of the through-holes 42, 43, and 44 by
means of electroless plating or the like. The electrode material is
then removed from the end faces 41a, 41b, 41e, 41f, 41i, and 41j.
The dielectric block 41 has side-wall through-holes 49, 50, and 51,
each extending from the central parts of the inner walls of the
respective through-holes 42, 43, and 44 between their opposing ends
to the upper surfaces 41c, 41g, and 41k (where surfaces 41e, 41g,
and 41k are parts of the outer surface of the dielectric block 41).
Connection conductors 52, 53, and 54 are formed on the inner walls
of the respective side-wall through-holes 49, 50, and 51 such that
the central parts of the respective inner conductors 45, 46, and 47
between the two opposing ends are connected to the outer conductor
48 via the connection conductors 52, 53, and 54. These connection
conductors 52, 53, and 54 may be formed at the same time as the
inner conductors 45, 46, and 47 and the outer conductor 48 by
subjecting the side-wall through-holes 49, 50, and 51 to the
plating process for forming the inner conductors 45, 46, and 47 and
the outer conductor 48.
In the dielectric filter having the structure described above, the
end of the inner conductor 45 on the side of the first end face 41a
of the sub-block LW3 of the dielectric block 41 is used as an input
terminal IN, while the end of the inner conductor 47 on the side of
the second end face 41i of the sub-block LW5 of the dielectric
block 41 is used as an output terminal OUT, as shown in FIG. 13.
The outer conductor 48 is connected to a ground line. Thus, the
dielectric filter of the present embodiment can be represented by
an equivalent circuit shown in FIG. 14.
In this equivalent circuit, R7 and R8 are two resonators formed
with the inner conductor 45 divided into two sections at the center
between its two ends, R9 and R10 are two resonators formed with the
inner conductor 46 divided into two sections at the center between
its two ends, and R11 and R12 are two resonators formed with the
inner conductor 47 divided into two sections at the center between
its two ends. L4 is an inductor associated with the connection
conductor 52, L5 is an inductor associated with the connection
conductor 53, and L6 is an inductor associated with the connection
conductor 54.
K79 is a phase shifter formed between a part of K79 the sub-block
LW3 of the dielectric block 41 in the region extending from the
first end face 41a to the connection conductor 52 and a part of the
sub-block LW4 in the region extending from the second end face 41f
to the connection conductor 53. K911 is a phase shifter formed
between a part of the sub-block LW4 of the dielectric block 41 in
the region extending from the second end face 41f to the connection
conductor 53 and a part of the sub-block LW5 in the region
extending from the first end face 41i to the connection conductor
54.
As described above, the dielectric filter includes: the dielectric
block 41 composed of the sub-block LW3 with two opposing end faces
namely the first end face 41a and the second end face 41b, the
sub-block LW4 with two opposing end faces namely the first end face
41e and the second end face 41f, and the sub-block LW5 with two
opposing end faces namely the first end face 41i and the second end
face 41j. The dielectric block 41 also includes the three
through-holes 42, 43, and 44 wherein the through-hole 42 is formed
between the first end face 41a and the second end face 41b of the
sub-block LW3 of the dielectric block 41, the through-hole 43 is
formed between the first end face 41e and the second end face 41f
of the sub-block LW4, and the through-hole 44 is formed between the
first end face 41i and the second end face 41j of the sub-block
LW5. The dielectric block 41 also includes the three inner
conductors 45, 46, and 47 formed on the inner walls of the
respective through-holes 42, 43, and 44 wherein both ends of each
inner conductor 45, 46, 47 are electrically open-circuited; the
outer conductor 48 formed on the outer surface of the dielectric
block 41; and the three connection conductors 52, 53, and 54 by
which the central parts of the respective inner conductors 45, 46,
and 47 are connected to the output conductor 48. As shown in FIG.
14, three filter stages are formed in the dielectric filter having
the above structure (a first filter stage is composed of the
resonators R7 and R8 and the inductor L4, a second filter stage is
composed of the resonators R9 and R10 and the inductor L5, and a
third filter stage is composed of the resonators R11 and R12 and
the inductor L6). These three filter stages are connected from one
stage to the next via the phase shifters K79, and K911. The filter
stage including the resonator R9 is connected to the input terminal
IN and the filter stage including the resonator R11 is connected to
the output terminal OUT. Therefore, in this dielectric filter
having the above structure, the signal given at the input terminal
IN is changed in phase by about 90.degree. via the phase shifter
K79 and by another 90.degree. via the phase shifter K911 and the
phase-shifted signal appears at the output terminal OUT.
The dielectric filter with the above structure has two pass-bands
separated by a trap frequency ft, as shown in FIG. 15, wherein
attenuation occurs at edges of the pass-bands. The trap frequency
ft and the frequency-attenuation characteristics of the two
pass-bands located at either side of the trap frequency ft are
determined by properly selecting the relative dielectric constant
of the dielectric block 41, the lengths of the inner conductors 45,
46, and 47, and the inductances associated with the connection
conductors 52, 53, and 54. Since the dielectric filter of the
present embodiment has three filter stages, it is possible to
adjust the frequency bandwidth of the trap band, and a greater
attenuation can be achieved within the trap band. Thus, this
dielectric filter acts as a high-performance band-elimination
filter having two pass-bands at either side of the trap frequency
ft. In other words, the dielectric filter behaves both as a
band-pass filter and a band-elimination filter.
Although not shown here in the figure, end face electrodes similar
to those shown in FIGS. 5 or 6 may be formed on the end face 41a of
the sub-block LW3 and the end face 41i of the sub-block LW5 such
that the end face electrode on the end face 41a is connected to the
inner conductor 45 to serve as an input terminal IN and the end
face electrode on the end face 41i is connected to the inner
conductor 47 to serve as an output terminal OUT. In this case, as
in the example shown in FIGS. 5 or 6, the outer conductor 48 may
have additional portions which extend on the end faces 41a and 41i
and which are electrically isolated from the end face electrodes.
The other end faces may be covered with portions extending from the
outer conductor 48 as in the example shown in FIG. 7. The addition
of these end face electrodes readily permits a signal line to be
connected to the inner conductors. That is, the connection can be
accomplished simply by connecting the signal line to the respective
end face electrodes serving as the input terminal IN and the output
terminal OUT. Furthermore, in the case where the outer conductor 48
is formed by means of plating, the above structures having the end
face electrodes allow the conductors to be more easily formed,
because these structures lead to a reduction in the area of the
electrode material which should be removed after the plating
process.
In an alternative mode, the inner conductors 45, 46, and 47 may
also be formed in such a manner as to have a length which does not
reach either the first end faces 41a, 41e, 41i or the second end
faces 41b, 41f, 41j. In this case, the outer conductor 48 may be
formed in such a manner as to have additional portions which extend
over the whole areas of the first end faces 41a, 41e, 41i and the
second end faces 41b, 41f, 41j and which further extend into the
through-holes 42, 43, and 44. This structure leads to an
improvement in the shielding performance of the dielectric
filter.
In the above structures, the side-wall through-holes 49, 50, and 51
are formed, as described above, in such a manner as to extend from
the corresponding central parts of the inner walls of the
respective through-holes 42, 43, and 44 (between their two opposing
ends) to the outer surface of the dielectric block 41. The
connection conductors 52, 53, and 54 are formed on the inner walls
of the respective side-wall through-holes 49, 50, and 51 in such a
manner that the central parts of the inner conductors 45, 46, and
47 between the two opposing ends are connected to the outer
conductor 48 via the connection conductors 52, 53, and 54. Herein
the central parts between the two ends need not necessarily be
located at the exact geometric centers but may to be located within
ranges around the exact geometric centers as long as the filter has
a good frequency characteristic as described herein, for example in
FIG. 15.
In the dielectric block 41, as described above, the length LE3
between the first end face 41a and the second end face 41b of the
sub-block LW3, the length LE4 between the first end face 41e and
the second end face 41f of the sub-block LW4, and the length LE5
between the first end face 41i and the second end face 41j of the
sub-block LW5 are equal to one another. Further, the three
sub-blocks LW3, LW4, and LW5 are shifted in longitudinal directions
by half the length of one sub-block relative to adjacent
sub-blocks. However, these conditions are not restrictive, and some
deviations are permitted to obtain a frequency characteristic
similar to that shown in FIG. 15. That is, in the dielectric block
41 of the present embodiment, a certain tolerance is allowed in the
degree to which the length LE3, LE4, and LE5 match. Further, the
three sub-blocks LW3, LW4, and LW5 may be shifted in longitudinal
directions (toward the opposite end face) by half the length of one
sub-block relative to the adjacent sub-block within a certain
tolerance. Similarly, a certain tolerance is allowed in the degree
to which the widths W3, W4, and W5 of the sub-blocks LW3, LW4, and
LW5 match.
FIG. 16 is a perspective view of a fourth embodiment of a
dielectric filter 400 according to the present invention, while a
plan view thereof is shown in FIG. 17. As shown in these figures,
the dielectric filter is composed of a dielectric block 61 made up
of a ceramic material including four sub-blocks LW6, LW7, LW8, and
LW9 formed in an integral fashion and having equal lengths LE6,
LE7, LE8, and LE9 and equal widths W6, W7, W8, and W9. The four
sub-blocks LW6, LW7, LW8 and LW9 are shifted in longitudinal
directions by half the length LE6, LE7, LE8, or LE9 relative to
adjacent sub-blocks.
The sub-block LW6 has two opposing end faces, namely a first end
face 61a and a second end face 61b, located at either end of the
length LE6, and also has two opposing sides, namely an upper face
61c and a lower face 61d which are perpendicular to the end faces
61a and 61b. The sub-block LW7 has two opposing end faces, namely a
first end face 61e and a second end face 61f located at either end
of the length LE7, and also has two opposing sides, namely an upper
face 61e and a lower face 61f which are perpendicular to the end
faces 61e and 61f. The sub-block LW8 has two opposing end faces,
namely a first end face 61i and a second end face 61j, located at
either end of the length LE8, and also has two opposing sides,
namely an upper face 61k and a lower face 61l which are
perpendicular to the end faces 61i and 61j. The sub-block LW9 has
two opposing end faces, namely a first end face 61m and a second
end face 61n, located at either end of the length LE9, and also has
two opposing sides, namely an upper face 61p and a lower face 61q
which are perpendicular to the end faces 61m and 61n. The first end
faces 61a, 61e, 61i, and 61m of the respective sub-blocks LW6, LW7,
LW8, and LW9 are located on a same side, while the second end faces
61b, 61f, 61j, and 61n are located on another same side. The
sub-blocks LW7 and LW9 are shifted in the longitudinal direction by
half the length LE7 or LE9 relative to the sub-blocks LW6 and LW8
toward the first end faces 61a and 61i. The upper faces 61c, 61g,
61k, and 61p of the respective sub-blocks LW6, LW7, LW8, and LW9
lie in one plane, and the lower faces 61d, 61h, 61l, and 61q lie in
another plane.
The dielectric block 61 has through-holes 62, 63, 64, and 65
wherein the through-hole 62 is formed between the first and second
end faces 61a and 61b of the sub-block LW6, the through-hole 63 is
formed between the first and second end faces 61e and 61f of the
sub-block LW7, the through-hole 64 is formed between the first and
second end faces 61i and 61j of the sub-block LW8, and the
through-hole 65 is formed between the first and second end faces
61m and 61n of the sub-block LW9. Inner conductors 66, 67, 68, and
69 are formed on the inner walls of the respective through-holes
62, 63, 64, and 65. An outer conductor 70 is formed over the whole
outer surface of the dielectric block 61 except the end faces 61a,
61b, 61e, 61f, 61i, 61j, 61m, and 61n. In this structure, the
respective inner conductors 66, 67, 68, and 69 are not connected,
at either end, to the outer conductor 70, and thus the inner
conductors 66, 67, 68, and 69 are electrically open-circuited. The
inner conductors 66, 67, 68, and 69 and the outer conductor 70 may
be formed, for example, by disposing an electrode material such as
Cu over the whole surface of the dielectric block 61 including the
inner walls of the through-holes 62, 63, 64, and 65 by means of
electroless plating or the like. The electrode material is then
removed from the end faces 61a, 61b, 61e, 61f, 61i, 61j, 61m, and
61n.
The dielectric block 61 has respective side-wall through-holes 71,
72, 73, and 74 extending from the central parts of the inner walls
of the respective through-holes 62, 63, 64, and 65 (between their
two ends) to the upper surfaces 61c, 61g, 61k, and 61p (where upper
surfaces 61c, 61g, 61k and 61p are parts of the outer surface of
the dielectric block 61). Connection conductors 75, 76, 77, and 78
are formed on the inner walls of the respective side-wall
through-holes 71, 72, 73, and 74 so that the central parts of the
respective inner conductors 66, 67, 68, and 69 between the
corresponding two ends are connected to the outer conductor 70 via
the connection conductors 75, 76, 77, and 78. These connection
conductors 75, 76, 77, and 78 may be formed at the same time as the
inner conductors 66, 67, 68, and 69 and the outer conductor 70 by
subjecting the side-wall through-holes 71, 72, 73, and 74 to the
plating process for forming the inner conductors 66, 67, 68, and 69
and the outer conductor 70.
In the dielectric filter having the structure described above, the
end of the inner conductor 66 on the side of the first end face 61a
of the sub-block LW6 of the dielectric block 61 is used as an input
terminal IN, while the end of the inner conductor 69 on the side of
the second end face 61n of the sub-block LW9 of the dielectric
block 61 is used as an output terminal OUT, as shown in FIG. 17.
The outer conductor 70 is connected to a ground line. Thus, the
dielectric filter of the present embodiment can be represented by
an equivalent circuit shown in FIG. 18.
In this equivalent circuit, R13 and R14 are two resonators formed
with the inner conductor 66 divided into two sections at the center
between its two opposing ends, R15 and R16 are two resonators
formed with the inner conductor 67 divided into two sections at the
center between its two opposing ends, R17 and R18 are two
resonators formed with the inner conductor 68 divided into two
sections at the center between its two opposing ends, and R19 and
R20 are two resonators formed with the inner conductor 69 divided
into two sections at the center between its two opposing ends. L7
is an inductor associated with the connection conductor 75, L8 is
an inductor associated with the connection conductor 76, L9 is an
inductor associated with the connection conductor 77, and L10 is an
inductor associated with the connection conductor 78.
K1315 is a phase shifter formed between a part of the sub-block LW6
of the dielectric block 61 in the region extending from the first
end face 61a to the connection conductor 75 and a part of the
sub-block LW7 in the region extending from the second end face 61f
to the connection conductor 76. K1517 is a phase shifter formed
between a part of the sub-block LW7 in the region extending from
the second end face 61f to the connection conductor 76 and a part
of the sub-block LW8 in the region extending from the first end
face 61i to the connection conductor 77. K1719 is a phase shifter
formed between a part of the sub-block LW8 in the region extending
from the first end face 61i to the connection conductor 77 and a
part of the sub-block LW9 in the region extending from the second
end face 61n to the connection conductor 78.
As described above, the dielectric filter includes: the dielectric
block 61 composed of the sub-block LW6 with two opposing end faces
namely the first end face 61a and the second end face 61b, the
sub-block LW7 with two opposing end faces namely the first end face
61e and the second end face 61f, the sub-block LW8 with two
opposing end faces namely the first end face 61i and the second end
face 61j, and the sub-block LW9 with two opposing end faces namely
the first end face 61m and the second end face 61n. The dielectric
block 61 also includes the four through-holes 62, 63, 64, and 65
wherein the through-hole 62 is formed between the first end face
61a and the second end face 61b of the sub-block LW6 of the
dielectric block 61, the through-hole 63 is formed between the
first end face 61e and the second end face 61f of the sub-block
LW7, the through-hole 64 is formed between the first end face 61i
and the second end face 61j of the sub-block LW8, and the
through-hole 65 is formed between the first end face 61m and the
second end face 61n of the sub-block LW9. The dielectric block 61
also includes the four inner conductors 66, 67, 68, and 69 formed
on the inner walls of the respective through-holes 62, 63, 64, and
65 wherein both ends of each inner conductor 66, 67, 68, and 69 are
electrically open-circuited. The dielectric block 61 also includes
the outer conductor 70 formed on the outer surface of the
dielectric block 61; and the four connection conductors 75, 76, 77,
and 78 by which the central parts of the respective inner
conductors 66, 67, 68, and 69 are connected to the output conductor
70.
As shown in FIG. 18, four filter stages are formed in the
dielectric filter having the above structure (a first filter stage
is composed of the resonators R13 and R14 and the inductor L7, a
second filter stage is composed of the resonators R15 and R16 and
the inductor L8, a third filter stage is composed of the resonators
R17 and R18 and the inductor L9, and a fourth filter stage is
composed of the resonators R19 and R20 and the inductor L10). These
four filter stages are coupled from one stage to a following stage
via the respective phase shifters K1315, K1517, and K1719. The
filter stage including the resonator R13 is connected to the input
terminal IN and the filter stage including the resonator R19 is
connected to the output terminal OUT. Therefore, in this dielectric
filter having the above structure, the signal input at the input
terminal IN is changed in phase by about 90.degree. via each phase
shifter K1315, K1517, K1719, and the phase-shifted signal appears
at the output terminal OUT.
The dielectric filter with the above structure has two pass-bands
separated by a trap frequency ft, as shown in FIG. 19, wherein
attenuation occurs at both edges of the two pass-bands. The trap
frequency ft and the frequency characteristics of the two
pass-bands located at either side of the trap frequency ft are
determined by properly selecting the relative dielectric constant
of the dielectric block 61, the lengths of the inner conductors 66,
67, 68, and 69, and the inductances associated with the connection
conductors 75, 76, 77, and 78. Since the dielectric filter of the
present embodiment has four filter stages, it is possible to adjust
the frequency bandwidth of the trap band, and a greater attenuation
can be achieved within the trap band. Thus, this dielectric filter
acts as a high-performance band-elimination filter having two
pass-bands at either side of the trap frequency ft. In other words,
the dielectric filter behaves both as a band-pass filter and a
band-elimination filter.
Although not shown here in the figure, end face electrodes similar
to those shown in FIGS. 5 or 6 may be formed on the first end face
61a of the sub-block LW6 and the second end face 61n of the
sub-block LW9 such that the end face electrode on the first end
face 61a is connected to the inner conductor 66 to serve as an
input terminal IN and the end face electrode on the second end face
61n is connected to the inner conductor 69 to serve as an output
terminal OUT. In this case, as in the example shown in FIGS. 5 or
6, the outer conductor 70 may have additional portions which extend
on the first end face 61a and the second end face 61n and which are
electrically isolated from the end face electrodes. The other end
faces may be covered with conductors extending from the outer
conductor 70 as in the example shown in FIG. 7. The addition of
these end face electrodes readily permits a signal line be
connected to the inner conductors. That is, the connection can be
accomplished simply by connecting the signal line to the respective
end face electrodes serving as the input terminal IN and the output
terminal OUT. Furthermore, in the case where the outer conductor 70
is formed by means of plating, the above structures having the end
face electrodes allow the conductors to be more easily formed,
because these structures lead to a reduction in the area of the
electrode material which should be removed after the plating
process.
In an alternative mode, as in the example shown in FIG. 7, the
inner conductors 66, 67, 68, and 69 may also be formed in such a
manner as to have a length which does not reach either the first
end faces 61a, 61e, 61i, 61m or the second end faces 61b, 61f, 61j,
61n. In this case, the outer conductor 70 may be formed in such a
manner as to have additional portions which extend over the whole
areas of the first end faces 61a, 61e, 61i, 61m and the second end
faces 61b, 61f, 61j, 61n and which further extend into the
through-holes 62, 63, 64, 65. This structure leads to an
improvement in the shielding performance of the dielectric
filter.
In the above structures, the respective side-wall through-holes 71,
72, 73 and 74 are formed, as described above, in such a manner as
to extend from the corresponding central parts of the inner walls
of the through-holes 62, 63, 64 and 65 (between their two opposing
ends) to the outer surface of the dielectric block 61. The
connection conductors 75, 76, 77 and 78 are formed on the inner
walls of the respective side-wall through-holes 71, 72, 73 and 74
in such a manner that the central parts of the inner conductors 66,
67, 68 and 69 (between the two opposing ends) are connected to the
outer conductor 70 via the connection conductors 75, 76, 77 and 78.
Herein the central parts between the two ends do not necessarily
need to be located at the exact geometric centers but are permitted
to be located within ranges around the exact geometric centers as
long as the filter has a good frequency characteristic, such as
that shown in FIG. 19.
In the dielectric block 61, as described above, the length LE6
between the first end face 61a and the second end face 61b of the
sub-block LW6, the length LE7 between the first end face 61e and
the second end face 61f of the sub-block LW7, the length LE8
between the first end face 61i and the second end face 61j of the
sub-block LW8, and the length LE9 between the first end face 61m
and the second end face 61n of the sub-block LW9 are equal to one
another. The four sub-blocks LW6, LW7, LW8, and LW9 are shifted in
position from one another in longitudinal directions by half the
length of one sub-block. However, these conditions are not
restrictive and some deviations are allowed to obtain a frequency
characteristic similar to that shown in FIG. 19. That is, in the
dielectric block 61 of the present embodiment, a certain tolerance
is allowed in the degree to which the length LE6 between the first
end face 61a and the second end face 61b of the sub-block LW6, the
length LE7 between the first end face 61e and the second end face
61f of the sub-block LW7, the length LE8 between the first end face
61i and the second end face 61j of the sub-block LW8, and the
length LE9 between the first end face 61m and the second end face
61n of the sub-block LW9 match one another. Further, the three
sub-blocks LW3, LW4, and LW5 may be shifted in longitudinal
directions (toward the opposite end face) by half the length of one
sub-block relative to the adjacent sub-block within a certain
tolerance. Similarly, the degree to which the widths W6, W7, W8,
and W9 of the sub-blocks LW6, LW7, LW8, and LW9 match may have a
certain tolerance.
FIG. 20 is a perspective view of a fifth embodiment of a dielectric
filter 500 according to the present invention. A plan view of FIG.
20 is shown in FIG. 21. FIG. 22 is a cross-sectional view taken
along line 22--22 of FIG. 20. As shown in these figures, the
dielectric filter is composed of a rectangular dielectric block 81
of a ceramic material, including a first sub-block LW10 and a
second sub-block LW11 having equal lengths LE10 and equal widths
W10 and W11, respectively, wherein the first and second sub-blocks
are formed in an integral fashion. A slit 82 with a length equal to
half the length LE10 is formed between the sub-blocks LW10 and LW11
in such a manner that the slit 82 extends from one end face toward
the central part of the dielectric block 81. This slit 82 serves as
a coupling preventing means for preventing electromagnetic coupling
between the sub-blocks LW10 and LW11.
The first sub-block LW10 has two opposing end faces, namely a first
end face 81a and a second end face 81b, located at either end of
the length LE10, and also has two opposing sides, namely an upper
face 81c and a lower face 81d, which are perpendicular to the end
faces 81a and 81b. The second sub-block LW11 has two opposing end
faces, a first end face 81e and a second end face 81f, located at
either end of the length LE10, and also has two opposing sides, an
upper face 81g and a lower face 81h, which are perpendicular to the
end faces 81e and 81f. The first end faces 81a and 81e of the
respective sub-blocks LW10 and LW11 are located on a same side and
lie in one plane, while the second end faces 81b and 81f are
located on an opposite same side and lie in another plane. The slit
82 is formed between these two sub-blocks LW10 and LW11 such that
it extends from the second end faces 81b and 81f to the central
part between the first and second end faces. The upper faces 81c
and 81g of the respective sub-blocks LW10 and LW11 lie in one
plane, and the lower faces 81d and 81h lie in another plane. The
first sub-block LW10 has a side face 81i, and the second sub-block
LW11 has a side face 81j, opposite to the side face 81i.
The dielectric block 81 has through-holes 83 and 84 wherein the
through-hole 83 is formed between the first end face 81a and the
second end face 81b of the first sub-block LW10, and the
through-hole 84 is formed between the first end face 81e and the
second end face 81f of the second sub-block LW11. The inner walls
of the through-holes 83 and 84 are covered with inner conductors 85
and 86, respectively. An outer conductor 87 is formed over the
whole outer surface of the dielectric block 81 except for the end
faces 81a and 81b of the first sub-block LW10 and except for a
terminal electrode of the second sub-block LW11 which will be
described in further detail later. Neither end of the inner
conductor 85 of the first sub-block LW10 is connected to the outer
conductor 87 and thus the inner conductor 85 is electrically
open-circuited at both ends. On the other hand, both ends of the
inner conductor 86 of the second sub-block LW11 are connected to
the outer conductor 87 and thus the inner conductor 86 is
electrically short-circuited at both ends. The inner conductor 86
of the second sub-block LW11 has a gap 88 at a central part between
the two outer opposing ends 81e, 81f, wherein open-circuited inner
ends thereof are formed at the gap 88. A capacitor is formed by the
two facing inner ends across the gap 88.
The inner conductors 85, 86 and the outer conductor 87 may be
formed, for example, from an electrode material such as Cu covering
the whole surface of the dielectric block 81 including the inner
walls of the slit 82 and the through-holes 83 and 84 by means of
electroless plating or the like, which is then removed from the end
faces 81a and 81b of the first sub-block LW10. The gap area at the
open-circuited inner ends 88 of the inner conductor 86 of the
second sub-block LW11 is preferably covered with a protection
material before starting the plating process so that no electrode
material is deposited on the gap area during the plating process.
Alternatively, the gap at the open-circuited inner ends 88 may be
formed by partially removing the electrode material after
depositing the electrode material over the whole inner wall of the
through-hole 84.
The dielectric block 81 has a side-wall through-hole 89 extending
from the central part between the two opposing ends of the inner
wall of the through-hole 83 of the first sub-block LW11 to the
upper face 81c of the first sub-block LW11, wherein the upper face
81c is a part of the outer surface of the dielectric block 81. The
inner wall of the side-wall through-hole 89 is covered with a
connection conductor 90 by which the central part between the two
opposing ends of the inner conductor 85 is connected to the outer
conductor 87. The connection conductor 90 may be formed at the same
time as the inner conductors 85 and 86 by subjecting the side-wall
through-hole 89 to the plating process when forming the inner
conductors 85 and 86 and the outer conductor 87.
The dielectric block 81 also has a side-wall through-hole 92
extending, from a location slightly shifted from a center position
toward the first end face 81e of the inner wall of the through-hole
84 of the second block LW11, to side face 81j of the second
sub-block LW11, wherein the side face 81j is a part of the outer
surface of the dielectric block 81. A terminal electrode 93 is
formed on the side face 81j, in an area around the side-wall
through-hole 92. A gap 94 is formed around the terminal electrode
93 so that the terminal electrode 93 is electrically isolated from
the outer conductor 87. The inner wall of the side-wall
through-hole 92 is covered with a connection conductor 95 so that
the terminal electrode 93 is connected via the connection conductor
95 to the part of the inner conductor 86 at the location slightly
shifted from the open-circuited inner ends 88 toward the first end
face 81e. The terminal electrode 93 may be obtained, for example,
by partially removing the outer conductor 87 to form the gap 94.
The connection conductor 93 may be formed, for example, by
subjecting the inner wall of the side-wall through-hole 92 to the
plating process when forming the inner conductors 85 and 86 and the
outer conductor 87.
In the dielectric filter having the structure described above, the
end of the inner conductor 85 on the side of the first end face 81a
of the first sub-block LW10 is used as an input terminal IN, while
the terminal electrode 93 formed on the second block LW11 is used
as an output terminal OUT, as shown in FIG. 21. The outer conductor
87 is connected to a ground line. Thus, the dielectric filter of
the present embodiment can be represented by an equivalent circuit
shown in FIG. 23.
In this equivalent circuit, R21 and R22 are two resonators formed
with the inner conductor 85 of the first sub-block LW10, the inner
conductor 85 being divided into two sections at the center between
the two ends. R23 is a resonator formed from a part of inner
conductor 86 of the second sub-block LW11, extending from the
second end face 81f to the open-circuited inner gap 88. R24 is a
resonator formed from the other part of inner conductor 86
extending from the first end face 81e to the inner end connected to
the connection conductor 95. L11 is an inductor associated with the
connection conductor 90. C1 is a capacitor formed between the
open-circuited inner ends of the inner conductor 86 at the gap 88.
K2124 is a phase shifter formed between a part of the first
sub-block LW10 of the dielectric block 81 extending from the first
end face 81a to the connection conductor 90, and a part of the
second sub-block LW11 of the dielectric block 81 extending from the
first end face 81e to the connection conductor 95.
As described above, the dielectric filter of the present embodiment
includes: the dielectric block 81 composed of the first sub-block
LW10 having two opposing end faces, namely the first end face 81a
and the second end face 81b, and the second sub-block LW11 having
two opposing end faces, namely the first end face 81e and the
second end face 81f; the through-hole 83 formed between the first
end face 81a and the second end face 81b of the first sub-block
LW10 of the dielectric block 81; the inner conductor 85 formed on
the inner wall of the through-hole 83, wherein both ends of the
inner conductor 85 are electrically open-circuited; the outer
conductor 87 formed on the outer surface of the dielectric block
81; the connection conductor 90 connecting the central part of the
inner conductor 85 to the outer conductor 87; the through-hole 84
formed between the first end face 81e and the second end face 81f
of the second sub-block LW11 of the dielectric block 81; and the
inner conductor 86 formed on the inner wall of the through-hole 84,
wherein both outer ends of the inner conductor 86 are electrically
short-circuited and the open-circuited inner ends 88 are formed at
the center of the inner conductor 86 at the gap 88.
As shown in FIG. 23, two filter stages are formed in the dielectric
filter having the above structure (a first stage is formed with the
resonators R21 and R22 and the inductor L11, and a second stage is
formed with the resonators R23 and R24 and the capacitor Cl). The
first filter stage is connected to the input terminal IN and the
second filter stage is connected to the output terminal OUT. These
two filter stages are connected to each other via the phase shifter
K2124. In this dielectric filter having the above structure, a
signal input at the input terminal IN is shifted in phase by about
90.degree. via the phase shifter K2124 and the phase-shifted signal
appears at the output terminal OUT.
The dielectric filter with the above structure has two pass-bands
separated by a trap frequency ft, as shown in FIG. 24, wherein
elimination occurs at edges of the pass-bands. The trap frequency
ft and the frequency-attenuation characteristics of the two
pass-bands located at either side of the trap frequency ft are
determined by properly selecting the relative dielectric constant
of the dielectric block 81, the lengths of the inner conductors 85
and 86, and the inductance associated with the connection conductor
90. Since the dielectric filter of the present embodiment has two
filter stages, it is possible to adjust the frequency bandwidth of
the trap band, and a greater attenuation can be achieved within the
trap band. Thus, this dielectric filter acts as a high-performance
band-elimination filter having two pass-bands at either side of the
trap frequency ft. In other words, the dielectric filter behaves
both as a band-pass filter and a band-elimination filter.
Although not shown here in the figure, an end face electrode
similar to those shown in FIGS. 5 or 6 may be formed on the first
end face 81a of the first sub-block LW10 such that the end face
electrode on the first end face 81a is connected to the inner
conductor 85 to serve as an input terminal IN. In this case, as in
the example shown in FIGS. 5 or 6, the outer conductor 87 may have
an additional portion which extends on the first end face 81a and
which is electrically isolated from the end face electrode. The
second end face 81b may be covered with a conductor extending from
the outer conductor 87 as in the example shown in FIG. 7. The
addition of the end face electrode readily permits a signal line to
be connected to the inner conductor. That is, the connection can be
accomplished simply by connecting the signal line to the end face
electrode. Furthermore, in the case where the outer conductor 87 is
formed by means of plating, the above structure having the end face
electrode allows the conductors to be more easily formed, because
the structure leads to a reduction in the area of the electrode
material which should be removed after the plating process.
In an alternative mode, as in the example shown in FIG. 7, the
inner conductor 85 may also be formed in such a manner as to have a
length which does not reach either the first end face 81a or the
second end face 81b. In this case, the outer conductor 87 may be
formed in such a manner as to have additional portions which extend
over the first end face 81a and the second end face 81b and which
further extend inward the through-hole 83. This structure leads to
an improvement in the shielding performance of the dielectric
filter.
In another mode, as shown in a fragmentary plan view of FIG. 25 and
also in a cross-sectional view of FIG. 26, taken along line 26--26
of FIG. 25, the through-hole 84 of the second sub-block LW11 may be
divided into two closed-end holes 84a and 84b separated by an
isolation wall 97 wherein the entire inner surfaces of both the
closed-end holes 84a and 84b are covered with inner conductors 86a
and 86b, respectively, and the closed ends at the isolation wall 97
act as open-circuited inner ends, like the open-circuited inner
ends shown in FIGS. 21 and 22. In this case, a capacitor is formed
with the two inner-end portions of the inner conductors 86a and 86b
isolated by the isolation wall 97. This structure allows the
open-circuited ends to be more easily formed than the structure
shown in FIGS. 20-22. The slit 82 may be filled with an
electrically conductive material such as metal plating.
In the above structure, the side-wall through-hole 89 is formed, as
described above, in such a manner as to extend from the central
part between the outer ends of the inner wall of the through-hole
83 to the upper face 81c of the first sub-block LW10, which is a
part of the outer surface of the dielectric block 81, and the
connection conductor 90 is formed on the inner surface of the
side-wall through-hole 89 in such a manner that the central part
between the outer ends of the inner conductor 85 is connected to
the outer conductor 87 via the connection conductor 90. Herein the
central part between the two ends does not necessarily need to be
located at the exact geometric center but can be located within a
range around the center as long as the filter has a good frequency
characteristic, such as that in FIG. 24. Furthermore, in the
present embodiment, although the inner conductor 86 of the second
sub-block LW11 has the gap 88 located at the center between the
outer ends, the location of the gap 88 may be within a certain
tolerance so long as the filter has a good frequency
characteristic. Similarly, the slit 82 may be formed at the center
within a positional tolerance. Furthermore, the widths W10 and W11
of the respective sub-blocks may be equal to each other within a
certain tolerance. Furthermore, the first end faces 81a and 81e of
the respective sub-blocks LW10 and LW11 may be flush with each
other within a certain positional tolerance, and the second end
faces 81b and 81f may be flush with each other within a certain
positional tolerance.
FIG. 27 is a perspective view of a sixth embodiment of a dielectric
filter 600 according to the present invention. A plan view of FIG.
27 is shown in FIG. 28. FIG. 29 is a cross-sectional view taken
along line 29--29 of FIG. 28. As shown in these figures, the
dielectric filter is composed of a rectangular dielectric block 101
of a ceramic material, including a first first-type sub-block LW12,
a second-type sub-block LW13, and a second first-type sub-block
LW14, wherein these sub-blocks all have equal lengths LE11, equal
widths W12, W13, and W14, respectively, and are formed in an
integral fashion. Slits 102 and 103 with a length equal to half the
length LE11 are formed between the sub-blocks LW12 and LW13 and
between the sub-blocks LW13 and LW14 in such a manner that the
slits 102 and 103 extend from one end face toward the central part
of the dielectric block 101. These slits 102 and 103 serve as
coupling preventing means for preventing electromagnetic coupling
between the sub-blocks LW12 and LW13 and between the sub-blocks
LW13 and LW14.
The first first-type sub-block LW12 has two opposing end faces,
namely a first end face 101a and a second end face 101b, located at
either end of the length LE11, and also has two opposing sides,
namely an upper face 101c and a lower face 101d, which are
perpendicular to the end faces 101a and 101b. The second-type
sub-block LW13 has two opposing end faces, namely a first end face
101e and a second end face 101f, located at either end of the
length LE11, and also has two opposing sides, namely an upper face
101g and a lower face 101h, which are perpendicular to the end
faces 101e and 101f. The second first-type sub-block LW1 has two
opposing end faces, namely a first end face 101i and a second end
face 101j, located at either end of the length LE11, and also has
two opposing sides, namely an upper face 101k and a lower face
101l, which are perpendicular to the end faces 101i and 101j. The
first first-type sub-block LW12 is located on one side of the
dielectric block 101, the second first-type sub-block LW14 is
located on the opposite side of the dielectric block 101, and the
second-type sub-block LW13 is located between these first-type
sub-blocks LW12 and LW14. The first end faces 101a, 101e, and 101i
of the respective sub-blocks LW12, LW13, and LW14 are located on a
same side and lie in one plane, while the second end faces 101b,
101f, and 101j are located on an opposite same side and lie in
another plane. The slits 102 and 103 are formed between the
sub-blocks LW12 and LW13 and between the sub-blocks LW13 and LW14,
respectively, such that they extend from the second end faces 101b,
101f, and 101j to the central parts between the first and second
end faces. The upper faces 101c, 101g, and 101k of the respective
sub-blocks LW12, LW13, and LW14 lie in one plane, and the lower
faces 101d, 101h, and 101l lie in another plane.
The dielectric block 101 has through-holes 104, 105, and 106
wherein the through-hole 104 is formed between the first end face
101a and the second end face 101b of the first first-type sub-block
LW12, the through-hole 105 is formed between the first end face
101e and the second end face 101f of the second-type sub-block
LW13, and the through-hole 104 is formed between the first end face
101i and the second end face 101j of the second first-type
sub-block LW14. The inner walls of these through-holes 104, 105,
and 106 are covered with inner conductors 107, 108, and 109,
respectively. An outer conductor 101 is formed over the whole outer
surface of the dielectric block 101 except for: (i) the first end
face 101a and the second end face 101b of the first first-type
sub-block LW12; and (ii) the first end face 101i and the second end
face 101j of the second first-type sub-block LW14.
Neither end of the inner conductor 107 of the first first-type
sub-block LW12 is connected to the outer conductor 110 and thus the
inner conductor 107 is electrically open-circuited at both ends.
Similarly, neither end of the inner conductor 109 of the second
first-type sub-block LW14 is connected to the outer conductor 110
and thus the inner conductor 109 is electrically open-circuited at
both ends. On the other hand, both ends of the inner conductor 108
of the second-type sub-block LW13 are connected to the outer
conductor 110 and thus the inner conductor 108 is electrically
short-circuited at both ends. The inner conductor 108 of the
second-type sub-block LW13 has a gap at a central part between the
two outer ends 101e, 101f, wherein open-circuited inner ends 111
are formed at the gap. A capacitor is formed by these two inner
ends 111 facing each other across the gap.
The inner conductors 107, 108, 109 and the outer conductor 110 may
be formed, for example, from an electrode material such as Cu
covering the whole surface of the dielectric block 101 including
the inner walls of the slits 102 and 103 and the through-holes 104,
105, and 106 by means of electroless plating or the like, which is
then removed from the first end face 101a and the second end face
101b of the first first-type sub-block LW12 and also from the first
end face 101i and the second end face 101j of the second first-type
sub-block LW14.
The dielectric block 101 has side-wall through-holes 112 and 113.
The side-wall through-hole 112 extends from the central part
between the two opposing ends of the inner wall of the through-hole
104 of the first first-type sub-block LW12 to the upper face 101c
of the first first-type sub-block LW12, wherein the upper face 101c
is a part of the outer surface of the dielectric block 101. The
side-wall through-hole 113 extends from the central part between
the two opposing ends of the inner wall of the through-hole 106 of
the second first-type sub-block LW14 to the upper face 101k of the
second first-type sub-block LW14, wherein the upper face 101k is a
part of the outer surface of the dielectric block 101. The inner
walls of the side-wall through-holes 112 and 113 are covered with
connection conductors 114 and 115, respectively, so that the
central parts between the two opposing ends of the respective inner
conductors 107 and 109 are connected to the outer conductor 110 via
these connection conductors 114 and 115. These connection
conductors 114 and 115 may be formed, for example, at the same time
as the inner conductors 107, 108, 109 and the outer conductor 110,
by subjecting the inner walls of the side-wall through-holes 112
and 113 to the plating process when forming the inner conductors
107, 108, 109 and the outer conductor 110.
In the dielectric filter having the structure described above, the
end of the inner conductor 107 on the side of the first end face
101a of the first first-type sub-block LW12 is used as an input
terminal IN, while the end of the inner conductor 109 on the side
of the first end face 101i of the second first-type sub-block LW14
is used as an output terminal OUT. The outer conductor 110 is
connected to a ground line. Thus, the dielectric filter of the
present embodiment can be represented by an equivalent circuit
shown in FIG. 30.
In this equivalent circuit, R25 and R26 are two resonators formed
with the inner conductor 107 of the first first-type sub-block
LW12, the inner conductor 107 being divided into two sections at
the center between the two ends. R27 and R28 are two resonators
formed from the inner conductor 108 of the second-type sub-block
LW13, the inner conductor 108 being divided into two sections at
the center between the two ends. R29 and R30 are two resonators
formed from the inner conductor 109 of the second first-type
sub-block LW14, the inner conductor 109 being divided into two
sections at the center between the two ends. L12 is an inductor
associated with the connection conductor 114 of the first
first-type sub-block LW12, and L13 is an inductor associated with
the connection conductor 115 of the second first-type sub-block
LW14. C2 is a capacitor formed between the open-circuited inner
ends 111 of the inner conductor 108 of the second-type sub-block
LW13.
K2528 is a phase shifter formed between a part of the first
first-type sub-block LW12 of the dielectric block 101 extending
from the first end face 101a to the connection conductor 114, and a
part of the second-type sub-block LW13 extending from the first end
face 101e to the open-circuited inner end ill of the inner
conductor 108. K2829 is a phase shifter formed between a part of
the second-type sub-block LW13 of the dielectric block 101
extending from the first end face 101e to the open-circuited inner
end 111 of the inner conductor 108, and a part of the second
first-type sub-block LW14 extending from the first end face 101i to
the connection conductor 109.
As described above, the dielectric filter of the present embodiment
includes: the dielectric block 101 composed of the first first-type
sub-block LW12 having the two opposing end faces namely the first
end face 101a and the second end face 101b, the second-type
sub-block LW13 having the two opposing end faces namely the first
end face 101e and the second end face 101f, the second first-type
sub-block LW14 having the two opposing end faces namely the first
end face 101i and the second end face 101j; the through-hole 104
formed between the first end face 101a and the second end face 101b
of the first first-type sub-block LW12 of the dielectric block 101;
the inner conductor 107 formed on the inner wall of the
through-hole 104 wherein both ends of the inner conductor 107 are
electrically open-circuited; the through-hole 106 formed between
the first end face 101i and the second end face 101j of the second
first-type sub-block LW14 of the dielectric block 101; the inner
conductor 109 formed on the inner wall of the through-hole 106
wherein both ends of the inner conductor 109 are electrically
open-circuited; the outer conductor 110 formed on the outer surface
of the dielectric block 101; the connection conductor 114 by which
the central part between the two opposing ends of the inner
conductor 107 of the first first-type sub-block LW12 is connected
to the outer conductor 110; the connection conductor 115 by which
the central part between the two opposing ends of the inner
conductor 109 of the second first-type sub-block LW14 is connected
to the outer conductor 110; the through-hole 105 formed between the
first end face 101e and the second end face 101f of the second-type
sub-block LW13 of the dielectric block 101; and the inner conductor
108 formed on the inner wall of the through-hole 105, wherein
electrically open-circuited inner ends 111 are formed at the center
of the inner conductor 108 while both outer ends of the inner
conductor 108 are electrically short-circuited.
As shown in FIG. 30, three filter stages are formed in the
dielectric filter having the above structure (a first stage is
formed with the resonators R25 and R26 and the inductor L12, a
second stage is formed with the resonators R27 and R28 and the
capacitor C2, and a third stage is formed with the resonators R29
and R30 and the inductor L13). These three filter stages are
coupled from one stage to the next via the respective phase
shifters K2528 and K2829. The filter stage including the resonator
R25 is connected to the input terminal IN and the filter stage
including the resonator R29 is connected to the output terminal
OUT. In this dielectric filter having the above structure, a signal
given at the input terminal IN is shifted in phase by about
90.degree. via each phase shifter K2528, K2829 and the
phase-shifted signal appears at the output terminal OUT.
The dielectric filter with the above structure has two pass-bands
separated by a trap frequency ft, as shown in FIG. 31, wherein
elimination occurs at edges of the pass-bands. The trap frequency
ft and the frequency characteristics of the two pass-bands located
at either side of the trap frequency ft are determined by properly
selecting the relative dielectric constant of the dielectric block
101, the lengths of the inner conductors 107, 108, and 109, and the
inductances associated with the connection conductors 114 and 115.
Since the dielectric filter of the present embodiment has three
filter stages, it is possible to adjust the frequency bandwidth of
the trap band and a greater attenuation can be achieved within the
trap band. Thus, this dielectric filter acts as a high-performance
band-elimination filter having two pass-bands at either side of the
trap frequency ft. In other words, the dielectric filter behaves
both as a band-pass filter and a band-elimination filter.
Although not shown here in the figure, end face electrodes similar
to those shown in FIGS. 5 or 6 may be formed on the first end face
101a of the first first-type sub-block LW12 and on the first end
face 101i of the second first-type sub-block LW14 such that the end
face electrode on the first end face 101a is connected to the inner
conductor 107 to serve as an input terminal IN and the end face
electrode on the first end face 101i is connected to the inner
conductor 109 to serve as an output terminal OUT. In this case, as
in the example shown in FIGS. 5 or 6, the outer conductor 110 may
have additional portions which extend on the first end face 81a and
which are electrically isolated from the end face electrode. The
second end faces 101b and 101j may be covered with conductors
extending from the outer conductor 110 as in the example shown in
FIG. 7. The addition of the end face electrodes readily permits a
signal line to be connected to the inner conductors. That is, the
connection can be accomplished simply by connecting the signal line
to the end face electrodes. Furthermore, in the case where the
outer conductor 110 is formed by means of plating, the above
structure having the end face electrodes allows the conductors to
be more easily formed, because the structure leads to a reduction
in the area of the electrode material which should be removed after
the plating process.
In an alternative mode, as in the example shown in FIG. 7, the
inner conductor 107 of the first first-type sub-block LW12 and the
inner conductor 109 of the second first-type sub-block LW14 may
also be formed in such a manner as to have a length which does not
reach either the first end faces 101a, 101i or the second end faces
101b, 101j. In this case, the outer conductor 110 may have
additional portions which extend over the first end faces 101a,
101i and the second end faces 101b, 101j and which further extend
inward the through-holes 104, 106. This structure leads to an
improvement in the shielding performance of the dielectric
filter.
In another mode, as shown in a fragmentary plan view of FIG. 32 and
also in a cross-sectional view of FIG. 33, taken along line 33--33
of FIG. 32, the through-hole 105 of the second-type sub-block LW13
may be divided into two closed-end holes 105a and 105b separated by
an isolation wall 116 wherein the entire inner surfaces of both the
closed-end holes 105a and 105b are covered with inner conductors
106a and 106b, respectively, and the closed ends at the isolation
wall 116 act as open-circuited inner ends 111 as the open-circuited
inner ends shown in FIGS. 28 and 29. In this case, a capacitor is
formed with the two inner-end portions of the inner conductors 106a
and 106b isolated by the isolation wall 116. This structure allows
the open-circuited ends to be more easily formed than the structure
shown in FIGS. 27-29. The slits 102 and 103 may be filled with an
electrically conductive material such as a metal plate.
In the above structure, the side-wall through-hole 112 of the first
first-type sub-block LW12 and the side-wall through-hole 113 of the
second first-type sub-block LW14 are formed, as described above, in
such a manner that they extend from the central part between the
outer ends of the inner wall of the through-hole 104 or 109 to the
upper face 101c of the first first-type sub-block LW12 or to the
upper face 101k of the second first-type sub-block LW14 wherein the
upper faces 101c and 101k are parts of the outer surface of the
dielectric block 101. The connection conductors 114 and 115 are
formed on the inner surfaces of the side-wall through-holes 112 and
113 so that the central parts between the outer ends of the inner
conductors 107 and 109 are connected to the outer conductor 110 via
the connection conductors 114 and 115. Herein the "central part"
between the two ends does not necessarily need to be located at the
exact geometric center but can be located within a range around the
center as long as the filter has a good frequency characteristic,
such as shown herein. Furthermore, in the present embodiment,
although the inner conductor 108 of the second-type sub-block LW13
has the open-circuited inner ends 111 located at the center between
the outer ends, the location of the open-circuited inner ends 88
may have a certain tolerance so long as the filter has a good
frequency characteristic. Similarly, the slits 102 and 103 may be
formed at the centers within a positional tolerance. Furthermore,
the widths W12, LW13, and W14 of the respective sub-blocks may be
equal to one another within a certain tolerance. Furthermore, the
equality of the first end faces 101a, 101e, 101j of the respective
sub-blocks LW12, LW13, and LW14 may have a certain positional
tolerance, and the second end faces 101b, 101f, 101j may be flush
with one another within a certain positional tolerance.
Although, the dielectric filter of the present invention is
described above with reference to preferred embodiments, the
present invention is not limited to the details described, but
various modifications and changes may be made. For example although
in the specific embodiment described above in conjunction with
FIGS. 12 and 13, the dielectric block 41 is composed of three
sub-blocks LW3, LW4, and LW5 which are shifted in position in
longitudinal directions by half the length LE3, LE4, or LE5, the
dielectric block 41 may also be formed into a rectangular shape as
shown in FIG. 34 to achieve a dielectric filter having an
equivalent circuit similar to that shown in FIG. 14 and thus having
a similar characteristic to that shown in FIG. 15. This structure
will be described in greater detail below. In FIG. 34, similar
parts or elements to those of FIGS. 12 and 13 are denoted by
similar reference numerals, and they are not described herein in
further detail.
In the dielectric filter shown in FIG. 34, the dielectric block 41
includes three sub-blocks LW3, LW4, and LW5 having equal widths W3,
W4, W5, respectively. These sub-blocks also have first end faces
41a, 41e, and 41i which are located on a same side and which lie in
one plane. The sub-blocks further have second end faces 41c, 41f,
and 41j which are located on an opposite side and which lie in
another plane. The dielectric block 41 also has slits 411 and 412
serving as electromagnetic coupling preventing structures formed
between the sub-blocks LW3 and LW4 and between the sub-blocks LW4
and LW5, respectively, wherein these slits 411 and 412 extend from
the second end faces 41c, 41f, and 41j toward the central parts
between opposite end faces. An outer conductor 48 is formed on the
inner walls of these slits 411 and 412.
In the dielectric filter having the structure described above, the
end of the inner conductor 45 on the side of the first end face 41a
of the sub-block LW3 is used as an input terminal IN, while the end
of the inner conductor 47 on the side of the first end face 41i of
the sub-block LW5 is used as an output terminal OUT.
In the structure shown in FIG. 34, instead of employing the slits
411 and 412, the electromagnetic coupling preventing structures may
also be realized by forming the respective through-holes 42, 43,
and 44 with a so-called step structure (not shown). In the step
structure, each through-hole 42, 43, 44 has a smaller diameter in
the region from the second end faces 41c, 41f, 41j to the center
between the two opposing ends than in the region from the center
between the two opposing ends to the first end faces 41a, 41e,
41i.
End face electrodes similar to those shown in FIGS. 5 or 6 may be
formed on the first end faces 41a and 41i such that the end face
electrode on the first end face 41a serves as an input terminal IN
and the end face electrode on the first end face 41i serves as an
output terminal OUT. In this case, as in the example shown in FIGS.
5 or 6, the outer conductor 48 may have additional portions which
extend onto the first end faces 41a and 41i while being
electrically isolated from the end face electrodes. The other end
faces may be covered with conductors extending from the outer
conductor 48 as in the example shown in FIG. 7. The slits 411 and
412 may be filled with an electrically conductive material such as
metal plating.
Although in the specific example shown in FIGS. 27 and 28, the
dielectric filter includes a rectangular-shaped dielectric block
101 composed of three sub-blocks LW12, LW13, and LW14, the
dielectric block 101 may also be formed into the shape shown in
FIG. 35 to achieve a dielectric filter having an equivalent circuit
similar to that shown in FIG. 30 and thus having a similar
characteristic to that shown in FIG. 31. This structure will be
described in greater detail below. In FIG. 35, similar parts or
elements to those of FIGS. 27 and 28 are denoted by similar
reference numerals, and they are not described herein in further
detail.
In the dielectric filter shown in FIG. 35, the dielectric block 101
includes three sub-blocks LW12, LW13, and LW14 having equal widths
W12, W13, W14, respectively. These three sub-blocks LW12, LW13, and
LW14 are shifted in position relative to adjacent sub-blocks in
longitudinal directions by half the length LE11, LE12, or LE13
(toward end faces).
In this structure, the end of the inner conductor 107 on the side
of the first end face 101a of the sub-block LW12 is used as an
input terminal IN, while the end of the inner conductor 109 on the
side of the first end face 101i of the sub-block LW14 is used as an
output terminal OUT. End face electrodes similar to those shown in
FIGS. 5 or 6 may be formed on the first end faces 101a and 101i
such that the end face electrode on the first end face 101a serves
as an input terminal IN and the end face electrode on the first end
face 101i serves as an output terminal OUT. In this case, as in the
example shown in FIGS. 5 or 6, the outer conductor 110 may have
additional portions which extend onto the first end faces 101a and
101i and are electrically isolated from the end face electrodes.
The second end faces 101b and 101j may be covered with conductors
extending from the outer conductor 110 as in the example shown in
FIG. 7.
As described above, in the dielectric filter according to first to
fifth aspects of the present invention, the dielectric filter
includes the connection conductor for connecting the central part
of the inner conductor between its opposing ends to the outer
conductor. This structure allows the dielectric filter having the
single dielectric block to behave as a band-elimination filter
having band-pass regions at either side of the trap frequency
wherein elimination occurs at both band edges of the pass-bands.
Since such filter characteristics can be realized using only the
single dielectric block, it is becomes easier to mount the
dielectric filter on a circuit board.
In the dielectric filter according to the second aspect, the
connection conductor is disposed in the side-wall through-hole such
that the central part of the inner conductor is connected to the
outer conductor via the connection conductor thereby ensuring that
the inductor has a stable inductance.
In the dielectric filter according to the third aspect, the
dielectric filter includes a plurality of filter stages. This makes
it possible to adjust the frequency bandwidth of the trap band, and
a great attenuation can be achieved within the trap band. The
dielectric filter has pass-bands centered around the trap band,
wherein excellent elimination characteristics are achieved at the
edges of the pass-bands. Furthermore, the dielectric block is
constructed with a plurality of sub-blocks each having a
through-hole in such a manner that the sub-blocks are shifted in
position relative to each other in longitudinal directions so that
undesirable coupling among the different filter stages is prevented
thereby ensuring that the dielectric filter exhibits stable and
excellent filtering characteristics.
In the dielectric filter according to the fourth aspect, the
dielectric filter includes a plurality of filter stages. This makes
it possible to adjust the frequency bandwidth of the trap band, and
a great attenuation can be achieved within the trap band. The
dielectric filter has pass-bands centered around the trap band,
wherein excellent elimination characteristics are achieved at the
edges of the pass-bands. Furthermore, the dielectric block is
constructed with a plurality of sub-blocks each having a
through-hole wherein an electromagnetic coupling preventing
structure is provided between adjacent sub-blocks so that
undesirable coupling among the different filter stages is prevented
thereby ensuring that the dielectric filter exhibits stable and
excellent filtering characteristics.
In the dielectric filter according to the fifth aspect, the
connection conductor is disposed in the side-wall through-hole such
that the central part of the inner conductor is connected to the
outer conductor via the connection conductor thereby ensuring that
the inductor has a stable inductance and thus the dielectric filter
exhibits stable and excellent filtering characteristics.
In the dielectric filter according to sixth to eighth aspects of
the present invention, the dielectric filter includes the first
sub-block in which the central part of the inner conductor of the
first sub-block is connected to the outer conductor via the
connection conductor and also includes the second sub-block
including the inner conductor having open-circuited inner ends
located at the center of the inner conductor. This structure allows
the dielectric filter having a single dielectric block to behave as
a band-elimination filter having pass-bands centered around the
trap frequency wherein excellent elimination characteristics are
achieved at the edges of the pass-bands. Since such filter
characteristics can be realized using only the single dielectric
block, it becomes easier to mount the dielectric filter on a
circuit board. Furthermore, since the dielectric filter includes a
plurality of filter stages it is possible to adjust the frequency
bandwidth of the trap band, and a great attenuation can be achieved
within the trap band. This also ensures that the dielectric filter
with the pass-bands centered around the trap frequency has
excellent elimination characteristics at the edges of the
pass-bands.
In the dielectric filter according to the sixth aspect, the
dielectric block is constructed with a plurality of sub-blocks each
having a through-hole wherein an electromagnetic coupling
preventing structure is provided between adjacent sub-blocks so
that undesirable coupling among the different filter stages is
prevented thereby ensuring that the dielectric filter exhibits
stable and excellent filtering characteristics.
In the dielectric filter according to the seventh aspect, the
dielectric block is constructed with a plurality of sub-blocks each
having a through-hole in such a manner that the sub-blocks are
shifted in position relative to each other in longitudinal
directions so that undesirable coupling among the different filter
stages is prevented thereby ensuring that the dielectric filter
exhibits stable and excellent filtering characteristics.
In the dielectric filter according to the eighth aspect, the
connection conductor is disposed in the side-wall through-hole such
that the central part of the inner conductor is connected to the
outer conductor via the connection conductor thereby ensuring that
the inductor has a stable inductance and thus the dielectric filter
exhibits stable and excellent filtering characteristics.
Although the present invention has been described in relation to
particular embodiments thereof, many other variations and
modifications and other uses will become apparent to those skilled
in the art. Therefore, the present invention is not limited by the
specific disclosure herein.
* * * * *